The present invention is directed to avionic systems for measuring altitude and range of an aircraft in general, and more particularly, to a compact laser altimeter system for obtaining precision above ground level (AGL) measurements for the aircraft.
Today's military and commercial aircraft desire more precise measurements of aircraft position and position information. Ground based RADAR systems and Global Positioning Systems (GPS) allow for precise positioning of an aircraft in latitude and longitude desirable for air traffic control, aircraft separation, and navigation. However, precise AGL measurements are often difficult to achieve with such systems, especially for applications in which precise placement above ground is needed. New levels of precision for altitude or AGL measurements, on the order of +/−6 inches (15 cm), for example, are often required for flight profiles ranging from hover, to nap of the earth (NOE) flight, and autonomous landing. Current aircraft altimeter systems generally can not achieve these precise measurements.
Recently, laser-based altimeters have been proposed for use on-board aircraft. This laser altimeter technology presents a significant advancement over radar altimeters as the ground registered data contains a higher level of resolution due to the narrow beam of the laser. However, the laser altimeters do pose certain concerns when applied to aircraft, especially with regard to the volume of the instrument attributed to the large number of optical elements contained therein. Another concern is directed to the ruggedness of the instrument in an aircraft flight environment. The optical elements of the laser altimeter are generally mounted on an optical bench, adjusted to be precisely aligned with respect to each other and secured in place. But, because of the of the vibration, shock and wide temperature variation encountered in aircraft flight, the optical elements have a tendency to become misaligned over time and thus, require constant maintenance. In bi-static laser altimeter configurations, back scattering of laser beam transmissions into a telescope portion is an additional concern.
The present invention is intended to overcome the aforementioned concerns of current laser altimeters by providing a compact laser altimeter which improves upon size, ruggedness and maintenance of the instrument as will become more evident from the following description.